Apparatus for contacting a preform rod to cause the preform rod to have a substantially straight longitudinal axis and a transverse cross section which is substantially circular and disposed concentrically about its longitudinal axis

ABSTRACT

In order to provide a substrate such as an optical preform rod (24) which is suitable for insertion into a tube and which has a transverse cross section that is substantially circular and disposed concentrically about a longitudinal axis of the substrate substantially along its entire length, a force-applying means such as a graphite roller (52) is adapted to be moved incrementally toward an axis of rotation (35) about which the preform rod is turned rototably. Movement is discontinued when there is an indication that the force-applying means has been in continuous engagement with the preform rod for at least a predetermined portion of the periphery of the rod. In a preferred embodiment, the engagement of the force-applying means and the preform rod is discontinued after a predetermined time, whereafter the force-applying means again is moved toward the axis of rotation. Cycles of engagement and disengagement are continued as relative motion is caused between the force-applying means and the preform rod in a direction along the axis of rotation.

This is a division of application Ser. No. 07/409,551 now U.S. Pat. No.5,030,266 filed Sep. 19, 1989 which is a divisional application of Ser.No. 07/247,984, filed on Sep. 22, 1988 which is a continuation of Ser.No. 06/928,436 which was filed on Nov. 7, 1986, now abandoned.

TECHNICAL FIELD

This invention relates to apparatus for adjusting the configuration ofoptical preforms. More particularly, it relates to apparatus for causinga preform rod which is used in a rod and tube process for providingoptical preforms to have a predetermined configuration along the lengthof the preform rod.

BACKGROUND INFORMATION

Optical fiber of the type used in communications is fabricated typicallyby heating and drawing a portion of an optical preform comprising arefractive core surrounded by a protective glass cladding. Presently,there are several known processes for fabricating preforms. The modifiedchemical vapor deposition (MCVD) process, which is described in U.S.Pat. No. 4,217,027 issued in the names of J. B. MacChesney, et al. onAug. 12, 1980 and assigned to Bell Laboratories, Inc., has been foundmost useful because the process enables large scale production ofpreforms which yield very low loss optical fiber.

During the fabrication of preforms by the MCVD process, precursor,reactant-containing gases, such as SiCl and GeCl, are passed through arotating substrate tube which is made of silica glass. A torch heats thetube from the outside as the precursor gases are passed therethrough,causing deposition of submicron-sized glass particles on the insidesurface of the tube. The torch is moved along the longitudinal axis ofthe tube in a plurality of passes to build up layer upon layer of glassto provide a preform tube. Once a sufficient number of layers have beendeposited, the preform tube is then heated to cause it to be collapsedto yield a preform or preform rod as it is often called.

Increased demand for optical fiber has prompted efforts to increase theproductivity of the MCVD process. However, the MCVD process rate islimited by the thickness of the wall of the substrate tube. To obtainoptical fiber having optimal geometrical and optical characteristics,the preform must have a core-to-cladding mass ratio within specifiedlimits. Increasing the mass of the substrate tube to obtain a largerpreform requires that the wall of the substrate tube be made thicker.However, increasing the thickness of the wall of the substrate tubereduces the rate of heat transfer to the reactant-containing gases,thereby increasing the time required to deposit each layer of glassparticulates. If the wall of the substrate tube is too thick, theninsufficient heat transfer may occur, which may result in the formationof bubbles or incomplete sintering.

One way in which the productivity of the MCVD process can be increasedis first to produce an undercladded preform, having a larger thandesired core-to-cladding mass ratio. This preform is inserted into aglass tube which is referred to as an overcladding tube and which isthen collapsed onto the preform. This is referred to as the rod and tubetechnique. It is desirable that any added eccentricity of material aboutthe preform core due to overcladding should be minimized.

If the undercladding is not substantially straight, difficulties areencountered when the rod is inserted into the tube. This also may leadto problems when the tube is collapsed on the rod. Contact of thepreform with the inside surface of the tube has not been found to bedetrimental for present proof test levels of interest. However, radialmisalignment between the overcladding tube and the undercladded preformshould be minimized, otherwise the resultant drawn fiber core may be tooeccentric which inhibits proper splicing of the drawn fiber to another.

Optical fiber preform tube straightening is not new. For example, inU.S. Pat. No. 4,477,273, methods and apparatus are used forstraightening and configuring an optical preform tube. A graphite rollerwhich is mounted on a carriage that supports a torch is moved manuallyinto engagement with the preform tube at one end thereof and then movedalong the tube with the torch during a collapse mode. However, themanual movement of a roller into engagement with a preform rod may beexcessive and it may become embedded in the rod to such an extent thatas it is moved with the torch it could be urged against a mass of thepreform rod and cause damage thereto.

What is needed and what does not appear to be available in the prior artare automatic methods and apparatus for causing a preform rod to besubstantially straight so that it is suitable for trouble-free insertioninto a tube in a rod and tube process. The sought-after methods andapparatus desirably should be adaptable to existing apparatus and becontrollable for a variety of conditions.

SUMMARY OF THE INVENTION

The foregoing problems of the prior art have been overcome by theapparatus of this invention. An elongated substrate which is made of aglass material and which is to be used as a source for an optical fiberis supported for rotation about an axis of rotation which extendsthrough end portions thereof. Then the substrate is caused to be turnedrotatably about the axis of rotation. Force-applying means is caused tobe moved toward the substrate while it is being moved in a directionalong the axis of rotation and while the substrate is being rotateduntil the substrate and the force-applying means engage each other. Asignal is provided when the force-applying means has remained inengagement continuously with a predetermined portion of the periphery ofthe rotating substrate. In response to the signal, the incrementalmovement of the force-applying means toward the axis of rotation isdiscontinued.

Should the substrate not be circular, or should its cross section beoffset from the axis of rotation through the end portions of thesubstrate, then as it rotates, a portion of it adjacent to theforce-applying means will be spaced more closely to the axis of rotationcausing disengagement of the force-applying means and the substrate andallowing the force-applying means to be moved further incrementallytoward the longitudinal axis. This disengagement of the force-applyingmeans causes the generation of the signal to be discontinued.

Each successive section of the substrate is determined to be acceptablewhen the generation of the signal is maintained for a predetermined timewhich equates to the continuous engagement of the force-applying meanswith a predetermined portion of the periphery of the substrate as thesubstrate is being rotated. As a result of this process, the substrateis caused to have a longitudinal axis which is substantially straightalong its length and which is substantially coincident with the axis ofrotation and a substantially circular cross section which is disposedconcentrically about the longitudinal axis.

An apparatus for causing a substrate of optical quality glass materialto be substantially straight and substantially circular includesfacilities for suspending the substrate for rotation about an axis ofrotation through end portions of the substrate and means for applyingforces to each successive increment of length of the substrate. Theforce-applying means is supported so that it can be moved incrementallyin a first direction toward the axis of rotation of the substrate and sothat normally it is biased in the first direction. Also, facilitiescause the force-applying means to be moved in a direction along the axisof rotation while it is being moved incrementally toward the axis ofrotation. Signal generation means is biased normally in a seconddirection opposite to the first direction.

In operation, the force-applying means is moved incrementally toward theaxis of rotation of the substrate until a portion of the rotatingsubstrate and the force-applying means are in engagement with eachother. This causes the signal generation means to be moved in the firstdirection and provide a signal to control facilities operably connectedto the force-applying means. The signal continues as long as theforce-applying means is held in suitable engagement with the substrate.During rotation, if any portion of the circumference of a length of thesubstrate is oval-shaped or if the cross-section of the substrate isoffset from the axis of rotation through the end portions of thesubstrate, the force-applying means may become disengaged therefrom andbe biased toward the axis of rotation causing the operation of signalsto be discontinued. Each portion of length of the substrate isdetermined to be acceptably straight and circular when the generation ofsignals continues for at least a predetermined time. When this conditionis met, the control facilities discontinue the incremental movement ofthe force-applying means toward the axis of rotation. The predeterminedtime is chosen to equate to the engagement of the force-applying meanswith the substrate for a predetermined portion of the periphery of thesubstrate during each excursion of the force-applying means toward thesubstrate.

In a preferred embodiment, the apparatus of this invention is used tostraighten and to configure an optical quality glass preform rod afterdeposition of glass-forming materials has occurred inside a tube andafter the tube has been collapsed into the rod. However, the apparatusmay be used in other ways, such as for example, during the entirecollapse mode. In this way, in each pass during collapse, thestraightness and circularity of the resulting preform rod is controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present invention will be more readily understoodfrom the following detailed description of specific enbodiments thereofwhen read in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an apparatus for providing an opticalpreform rod;

FIG. 2 is a view of a portion of a torch assembly, a portion of astraightening and configuring device and a temperature profile across azone of heat which is caused to traverse a preform rod;

FIG. 3 is an elevational view of a portion of the apparatus of FIG. 1which is used to reconfigure an optical preform rod;

FIG. 4 is a schematic view of a preform rod of one configuration duringreconfiguring with a straightening and configuring device in the form ofa roller;

FIG. 5 is an end view of the preform rod of FIG. 4 as it is beingrotated;

FIG. 6 is a schematic view of a preform rod having an expected amount ofoffset during reconfiguring with the roller;

FIG. 7 is an end view of the preform rod of FIG. 7 as it is beingrotated;

FIG. 8 is a schematic view of still another preform rod having asubstantial offset;

FIGS. 9A, 9B and 9C are end views of the rod of FIG. 8 at differentlocations along its length;

FIG. 10 is an exaggerated side elevational view of the roller inengagement with a portion of a preform rod having a substantial offset;

FIGS. 11 and 12 are end views of a preform rod having an oval-shapedconfiguration and of the preform rod after it has been adjusted byapparatus of this invention; and

FIG. 13 is a view of a preform rod, the configuration of which has beenadjusted in accordance with the apparatus of this invention, insertedinto an overcladding tube.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown an apparatus which is designatedgenerally by the number 20 which includes straightening and configuringapparatus 22 which is used to cause an elongated glass substrate such asa preform rod 24 having particular optical properties to havepredetermined geometrical characteristics. Those characteristics arethat it will have a substantially straight longitudinal axis, and atransverse cross section at each point along the longitudinal axis whichis substantially circular and which is disposed concentrically about thelongitudinal axis.

The apparatus 20 also includes apparatus for heating a glass substratetube (not shown) to provide the glass preform rod 24 from which aredrawn lightguide fibers. The heating of the tube is required in order tocause the reaction products of gases and/or dopants being fed into thetube to be fused to the inside wall of the tube to provide an opticallysuitable profile for communications use. See priorly identified U.S.Pat. No. 4,271,027. The heating of the glass tube is carried out whilegas phase reactants are delivered to the tube. A system for thisdelivery is disclosed in U.S. Pat. No. 4,276,243 which issued on Jun.30, 1981, in the name of F. P. Partus.

The apparatus 20 generally includes a lathe 32 having a headstock 33 anda tailstock 34 each of which is driven off a common shaft (not shown)and which are used to support rotatably end portions of a glass startingtube for rotation about an axis 35 which extends through spindles (notshown) of the lathe. End portions of the glass tube are held in thespindles of the lathe 32. The lathe 32 also includes a carriage 36 whichis mounted for reciprocal movement along the lathe between the headstock33 and the tailstock 34. Mounted on the carriage 36 is a torch assembly,which is designated generally by the numeral 40, and the straighteningand configuring apparatus 22. The torch assembly 40 is adapted to causea flow of combustible gases to produce flames which are directed towardthe glass tube. By confining the heat from the burning gases to adesired surface area of the tube, the torch assembly 40 establishes azone of heat 41 (see FIG. 2) having a temperature profile at the surfaceof the tube. The mounting of the torch assembly 40 on the carriage 36and its movement relative to the glass tube causes the zone of heat tobe moved along the length of the tube.

A description of an oxy-hydrogen torch assembly suitable for use withthe apparatus 20 is provided in U.S. Pat. No. 4,231,777 which issued onNov. 4, 1980 in the names of B. Lynch and F. P. Partus. Another torchassembly is disclosed in U.S. Pat. No. 4,477,244 which issued on Oct.16, 1984 in the names of J. R. Nis and C. R. Spainhour. The torchassembly 40 includes a housing 42 supported by a bracket 43 which issupported from a post 45 that is mounted on the carriage 36.

The mounting of the torch assembly 40 for movement relative to thecenterline of the lathe 32 which extends between the headstock 33 andthe tailstock 34 provides for a predetermined confinement of thesubstrate tube. The confinement of the tube is of help in the control ofthe temperature profile along successive portions of the glass tube asthe torch assembly is moved reciprocally along the length of therotating tube during a deposition mode.

After the substrate tube has experienced the deposition mode, it iscollapsed into a solid rod. This may be accomplished by reducing therotational speed from about 75 rpm to about 20 rpm and by increasing thetemperature of the hot zone to about 1800° C. For one-half of thecollapse mode, each pass is from right to left as viewed in FIG. 1. Thenthe tube is pinched off near the tailstock 34 and additional collapsepasses from left to right are used.

Going now to the preform tube straightening and configuring apparatus22, it is seen from FIGS. 1 and 3 that a force-applying means in theform of a contact device 50 is positioned adjacent to the torch assembly40. In a preferred embodiment, the contact device 50 includes a roller52 which is made of graphite. The roller 52 is mounted in a fixedposition in bearings 54--54 that are supported in a housing 56. Thecontact device may take other forms such as for example, a metallictube. Advantageously, the roller may be turned in the bearings to otherorientations after wear occurs in any one position.

The roller 52 is mounted in an apparatus designated generally by thenumeral 60 which is supported on the lathe carriage. As can best be seenin FIG. 3, the apparatus includes a 90° gearbox 62 which is driven by astepper motor 64. Extending from the gearbox 62 is a drive screw 66which has an upper end that mates with an internally threaded screwmember mounted in a platform 68. Movement of the platform 68 is guidedby four rods 70--70 which are connected to an underside of the platform68 and which are mounted for reciprocal movement within bores in thegearbox.

Attached to the platform 68 is a cantilevered base 72 having a fulcrum74 attached thereto and a U-shaped end portion 76. Mounted in an upperportion 78 of the U-shaped end portion 76 of the base and insulatedtherefrom is a first electrical contact 80. The electrical contact 80includes a depending portion 82 which extends toward the cantileveredbase 72.

Mounted pivotally on the fulcrum 74 is an arm 84. At one end portion 85of the arm 84 is mounted a second electrical contact 86 which extendstoward the first electrical contact 80 and which is insulated from thearm 84. The upper end of the second electrical contact 86 is spacedabout 0.018 cm from the lower end of the upper contact 80.

A counterweight 88 is adjustably positioned on the arm 84 between thefulcrum 74 and the second electrical contact 86. In a preferredembodiment, the distance from the end of the end portion 85 of the armto the center of the fulcrum is about twice the distance from the centerof the fulcrum to the opposite end of the arm. The counterweight 88causes the end portion 85 of the arm to be biased normally in a downwarddirection as viewed in FIG. 3. Downward movement of the end portion ofthe arm 84 is controlled by an adjustable stop 89 having an upper endwhich engages an underside of the arm 84.

At an opposite end portion 92 of the arm 84 is mounted a cradle 96. Thecradle 96 is adapted to support rotatably the housing 56 in which ismounted the roller 52. As seen in FIG. 3, the cradle 96 is positioned onthe arm 84 so that a transverse centerline of the roller is aligned witha longitudinal axis 100 of the preform rod 24 which is supported betweenthe headstock 33 and the tailstock 34 of the lathe 32. The counterweight88 causes the roller 52 to be biased upwardly as viewed in FIG. 3. Itwill be recalled that the end portions of the preform rod 24 are held inspindles of the lathe 32 with axes of rotation of the spindles beingaligned with each other.

Generally, the operation of the apparatus 22 is such that the platform68 is caused to be moved upwardly as seen in FIG. 3 to elevate theroller 52. When the roller 52 engages the preform rod 24, the arm 84 iscaused to be turned in a counterclockwise direction as viewed in FIG. 3.This causes the second electrical contact 86 to be moved upwardly toengage the depending portion 82 of the first electrical contact 80 andcomplete an electrical circuit (not shown) which controls the steppermotor. Because of the location of the fulcrum 74 along the arm, adownward movement of the roller 52 of only about 0.005 cm-0.008 cm willcause the second electrical contact to move upwardly through the 0.018cm gap and engage the first elecrtrical contact 80.

The electrical contacts 80 and 86 perform a dual function. Not only doestheir touching each other complete an electrical circuit, but they alsocooperate to provide a stop which is effective to discontinue the upwardmovement of the end portion 85 of the arm 84.

The electrical contacts 80 and 86 are connected to a programmablecontroller 90 which is connected to the stepper motor. The controller 90causes the platform 68 to be moved upwardly incrementally, and,responsive to the closing of the electrical contacts for a predeterminedtime, causes the upward movement to be discontinued.

In a preferred embodiment, the straightening and configuring portion 22of the apparatus 20 includes facilities for causing the surface thatengages the preform rod 24 to have a temperature that is substantiallybelow that of the preform rod. The housing 56 is adapted to hold acoolant such as deionized water which may be supplied by conduits (notshown) within the arm and cradle. The water is applied over the surfaceof the roller 52 to clean the surface thereof which engages the tube andto prevent the roller from adhering to the preform rod. The wateroverflows the sideplates and falls into a drain pan below (not shown).Also, the water forms an interface between the roller 52 and the rodwhich functions as a cushion to prevent damage to the surface of therod.

In the manufacture of the preform with the apparatus 20, a glass tube ispositioned in the lathe 32 with one of its ends in the headstock 33 andwith its other end connected by a welded joint (see FIG. 1) to anexhaust tube 97. The exhaust tube 97 is supported in the tailstock 34 ofthe lathe 32. The substrate tube is rotated as the torch assembly 40 ismoved in a plurality of passes in a direction from the headstock 33 tothe tailstock. During each pass, doped reactants are moved into the tubefrom its headstock end while spent gases are exhausted at the tailstockend. For a description of methods and apparatus for exhausting thesegases, see U.S. Pat. No. 4,278,459 which issued on Jul. 14, 1981 in thename of F. P. Partus.

Following deposition in a preferred embodiment, the passes of the firsthalf of the collapse mode occur. Then, the wall of the tube is pinchedtogether adjacent to its tailstock end. This prevents the entry ofmoisture and other contaminants into the tube while it is beingcollapsed. Then, the remaining passes of the collapse mode occur in theopposite direction.

During the collapse mode, the heating, at a higher temperature thanduring deposition, occurs as the torch assembly 40 is moved in a numberof passes from headstock to tailstock and in the second half of thecollapse mode from tailstock to headstock. At the end of each passduring the second half of the collapse mode, the carriage 36 is returnedrapidly to the tailstock for the beginning of another cycle.

After the substrate tube has been collapsed into a solid preform rod 24in the collapse mode, the graphite support roller 52 is caused to bemoved upwardly to engage the rotating preform rod 24 adjacent to thetailstock 34 (see FIG. 4) by the programmable contoller 90. Its verticalposition is a function of the orbit of the cross section of the rod. Theroller 52 is pushed partially into the preform rod and displacessoftened glass within the moving zone of heat a predetermined distance"d" (see FIG. 2) behind a centerline 101 of the torch assembly 40. Ifnecessary, the roller 52 is effective to force the rod into alignmentwith the axis of rotation between the headstock 33 and the tailstock 34.Accordingly, the roller 52 is adapted to urge successive increments oflength of the preform rod upwardly until each is disposed substantiallyconcentrically about the axis of rotation between the chucks of thelathe 32. During the straightening and configuring mode, the rotationalspeed of the preform rod 24 is about 75 rpm.

Parameters which are important to the method of straightening andconfiguring the preform rod 24 are the carriage speed and the rotationalspeed of the lathe spindles and the position of the engagement of thecontact device 50 with the preform rod 24 relative to the zone of heat.Also important is the temperature of the glass within the zone of heat41. This is a function of the delivery rates of hydrogen and oxygen tothe torch assembly 40. In the preferred embodiment, the delivery ofhydrogen to the torch assembly 40 is about 130 liters per minute and thedelivery of the oxygen is about 65 liters per minute.

The zone of heat 41 is formed in the vicinity of the torch assembly 40as the torch passes along the rod, but, as will be recalled, it isusually not centered with respect to the centerline 101 of the torch andtrails it (see FIG. 2). Up to a point, the distance, d, by which itsmaximum temperature lags the torch assembly 40 is a function of thevelocity of the torch assembly; the greater the velocity, the greaterthe trailing distance. Inasmuch as the preform rod 24 has a thicknessand the torch assembly 40 is moving along the rod, the zone of heat lagsthe torch assembly.

The contact device 50 must engage the preform rod 24 at a point wherethe glass is sufficiently soft so that it can be reconfigured. Also, thearrangement of the torch assembly 40 and the contact device must be suchthat the glass will take a set after its engagement with the roller 52.The point of engagement must not be at a point where subsequently theglass experiences a higher temperature, which would remove the set.

Inasmuch as the location of the zone of heat is difficult to ascertain,the roller 52 may be referenced to the centerline 101 (see FIG. 2) ofthe torch assembly 40. The distance "d" between the centerline of thetorch assembly 40 and a center axis 105 of the roller 52 is called thetrailing distance and occurs where the increment of length of glass issoft enough to be reconfigured without interfering with interior, lesssoft layers of the preform. Also, the increment engaged by the roller 52must be cool enough afterwards to retain that reconfiguration as thegraphite roller moves on to the next successive increment along thelength of the preform rod. In the preferred embodiment, the water whichis flowed over the graphite roller 52 provides ideally a moving coldzone which helps to establish a set in the preform rod which is beingstraightened progressively. In a preferred embodiment, the distance "d"is on the order of 3.5 cm. Should the distance exceed an establishedrange, the glass which is contacted by the roller 52 would be too coolto be successfully reconfigured.

The water cooling of the roller 52 is helpful in preventing the rollerfrom adhering to the glass tube. Also, the water is effective to flushany ablations caused by the flames from the tube. Otherwise, these couldcause dust particle accumulations which could become deposited on thegraphite roller and be impressed into the glass by the roller resultingin stress points in the preform rod and subsequent low strength fiber.

The manner of engagement and disengagement of the force-applying means,the roller 52, with the preform rod 24 is important to the successfulstraightening and reconfiguration of the preform rod. As can be seen inFIG. 4 of the drawings, the roller 52 is moved to a first jog stage 107as the carriage 36 is moving along the lathe bed at a velocity in therange of about 8 to 10 cm/minute. During this period of adjustment, thepreform rod 24 in the lathe is being caused to be turned at a rotationalvelocity of about 75 rpm. Another manner of stating the rotationalvelocity and one which will be more meaningful to an understanding ofthe invention is that the preform rod 24 is turned through about 0.5revolution in 0.4 second.

The first jog stage 107 in FIG. 4 is reached very rapidly by the roller52. It is caused to be reached by controlling the stepper motor 64through the programmable controller 90 to move the platform 68 upwardlytoward the axis of rotation of the preform rod until it reaches aposition which is designated "X" and which is always spaced from theaxis of rotation of the preform rod beyond the largest expected orbit ofany preform rod. The methods of this invention cause the reconfiguredpreform rod 24 to have a cross section which in area is substantiallyequal to the cross section before reconfiguring and which issubstantially circular. Also, as stated hereinbefore, the longitudinalaxis 100 of the reconfigured preform should be substantially straightwith the cross section disposed concentrically about the axis.

The stepper motor 64 is controlled to move the roller 52 upwardly firstin a gross mode which is the first jog stage 107 and then in a finetuning mode which is a second jog stage designated 109. In a normal finetuning mode, the stepper motor 64 is controlled to cause the roller tobe moved upwardly in steps of about 0.0036 cm, each. However, during thegross mode, a multiplier is used to cause each upward step to be about0.0108 cm. The gross mode is used to cause the roller 52 to move rapidlyfrom the reference position, "X", into initial engagement with thepreform rod 24. Initially, the preform rod 24 occupies the positionshown in solid lines in FIG. 4 and orbits about the axis of rotation 35as shown in FIG. 5. Desirably, the point of initial engagement with thepreform rod is just to one side of the pinch-off area (see FIG. 4). Ascan be seen in FIG. 5, the preform rod 24 has a slight offset whichcauses it to orbit slightly as the preform rod is turned rotatably.

After the initial engagement of the roller 52 with the preform rod andwhile the preform rod is orbiting slightly (see FIG. 5), the roller ismoved upwardly in 0.0036 cm steps during the fine tuning mode. Theincremental steps upwardly are made approximately in 0.1 to 0.2 secondintervals.

During the fine tuning mode, there occurs what is referred to as a 0.4second search. After the initial engagement of the roller 52 with thepreform rod, the roller is caused to be moved into the preform rod adistance of about 0.005 to 0.008 cm. As a result, the electrical contact86 is caused to be moved through the 0.0018 cm gap and engage the firstelectrical contact 80. When the roller 52 has been engaged with thepreform rod 24 continuously for 0.4 second, which corresponds to aboutone-half of a complete 360° rotation of the preform rod, it is assumedthat the cross section is circular at that location and that the axis issubstantially straight and in line with the centerline axis of rotation35 extending through the headstock 33 and the tailstock 34 of the lathe32. This engagement has taken place while the carriage 36 is being movedin a direction along the preform rod at the rate of about 9.6 cm/min.Approximately twenty times a second, the controller 90 looks for thesatisfaction of the 0.4 second search.

At this time, several alternatives are available. In one, the roller 52is caused to remain at its present level relative to the axis ofrotation 35 and no further adjustments are made. A variation of thiswould allow the roller 52 to be moved upwardly to reengage the preformrod 24 should disengagement occur as the roller traverses the rod. Inthe vast majority of times, either results in an acceptable preform rod.However, if for some reason, the point of initial engagement of theroller with the preform rod 24 is further toward the left, as seen inFIG. 4, in the necked-down area, the roller at a fixed spacing relativeto the axis of rotation may be moved against an increasingly large massof glass which could result in damage to the glass.

In the preferred embodiment, there is a constant cycling of the makingand breaking of the electrical contacts 80 and 86. After the 0.4 secondsearch has been satisfied, there is a pause for about 5.0 seconds duringwhich time the carriage 36 has advanced about 0.8 cm. After 5 secondshave elapsed, the platform 68 is moved downwardly to cause the roller 52to discontinue its engagement with the preform rod and the 0.4 secondsearch condition is not satisfied. Also, the electrical contact 86becomes disengaged from the electrical contact 80. Immediatelythereafter and as the carriage 36 is being moved in a direction alongthe preform rod 24, the roller 52 again is moved upwardly to restartanother cycle which includes a 0.4 second search. In other words, aftereach 0.4 second engagement of the roller 52 with the preform rod, thestepper motor 64 is controlled to cause the roller to become disengagedfrom the preform and so that the 0.4 second window condition is notcontinuously satisfied. When that occurs, the stepper motor 64 iscontrolled to cause the platform 68 and hence the roller 52 to be movedupwardly as the carriage is advanced along the preform rod until the 0.4second window condition again is satisfied. As a result, theconfiguration of the preform rod is monitored and adjusted continuously.

A further refinement may be used. If, in each 5 second window of timeduring which the roller 52 is held at a constant distance from the axis35, the roller becomes disengaged from the preform rod because ofresidual orbiting, for example, then the controller 90 causes the rolleragain to be moved upwardly to engage the rod.

What is important is that as the roller 52 engages the preform rod, itcauses the orbit of the rod to become smaller and smaller iterativelyuntil there is none. In a preferred embodiment, two reconfiguring passesare used. At that time, the preform rod has the sought after geometricalcharacteristics and the longitudinal axis 100 of the preform rod issubstantially coincident with the axis of rotation 35 (see phantom lineposition in FIGS. 4 and 5).

Viewing now FIGS. 6 and 7, there is shown a substrate rod 24 which has amore pronounced offset. The preform rod 24 in its initial configurationin FIG. 6 is shown in solid lines. Again, the roller 52 is caused to bemoved upwardly in a gross mode 107 from a position "X" to engage therod. However, because of the offset, the fine tuning mode 109 mayrequire substantially more 0.0036 cm upward jogs until the 0.4 secondwindow search is satisfied. This is due to the increased orbiting of thecross section of the rod causing the position of the roller to befarther spaced from the centerline of the spindles than before (seeorbiting rod shown in solid in FIGS. 6 and 7).

Also as seen in FIGS. 8 and 9, the preform rod 24 may have an even moresevere offset which causes an enlarged orbit. In such an instance, thefine tuning mode 109 requires even more jogs until the 0.4 window issatisfied which denotes that the rod is straightened at that location.Reference may be made to FIGS. 9A, 9B and 9C which show the position ofthe roller 52 with respect to the preform rod 24 at several positionsalong the length. As can be seen by comparing FIGS. 9A and 9B, theorbiting has decreased and at the location where FIG. 9C is taken thereis none. After reconfiguring, the preform rod 24, as shown by thecentral phantom line position in FIG. 8 has its longitudinal axissubstantially coincident with the axis of rotation 35. In FIG. 10, theposition of the roller 52 with respect to an offset portion of thepreform rod is shown. As the roller 52 is moved to the right, the rollercauses the rod to be straightened and to have a circular cross-sectionalconfiguration.

In FIGS. 11 and 12, there are shown views of an out-of-round preform rod24 and its reconfiguring with a force-applying means such as the roller52. As is seen in FIG. 11, the preform rod is somewhat oval-shaped sothat as it is rotated, it becomes disengaged with the roller 52 along alower portion of its periphery. This disengagement causes the controller90 to cause the platform to be moved upwardly until the roller 52 andpreform rod 24 again engage each other.

After it has been caused to be straightened by the apparatus 20 of thisinvention, the preform rod 24 is now ready for use in preparing apreform from which optical fiber is drawn. As is seen in FIG. 13, thereconfigured preform rod 24 is inserted into an overcladding tube 120whereafter the tube is caused to be collapsed onto the rod.Subsequently, optical fiber is drawn from the overcladded rod inaccordance with well known methods.

It is to be understood that the above-described arrangements are simplyillustrative of the invention. Other arrangements may be devised bythose skilled in the art which will embody the principles of theinvention and fall within the spirit and scope thereof.

What is claimed is:
 1. An apparatus for causing a preform rod from whichoptical fiber is to be drawn to have a substantially straightlongitudinal axis and to have a transverse cross section along the rodlength which cross section is substantially circular and which crosssection is disposed concentrically about the rod longitudinal axisnotwithstanding differing diameters among successive preforms to bestraightened by said apparatus, said apparatus comprising:supportingmeans for holding end portions of an elongated, glass,substantially-circular-cross-section preform rod so that the preform rodis capable of rotation about the rod axis of rotation which extendsthrough the end portions of the rod; means for causing the preform rodto be turned rotatably about the axis of rotation, the rotating of apreform rod which is not substantially straight causing portions of thepreform rod to be at a greater radial distance from the axis of rotationthan are other portions of the preform rod; a roller extendingtransversely of the axis of rotation, said roller being a means forengaging the longitudinal periphery of the preform rod to straighten thepreform rod and to cause the preform rod to be disposed concentricallyabout the axis of rotation; heating means for heating successiveincrements of length of the preform rod, said heating means and saidroller being positioned with respect to each other such that the preformrod is straightened by the roller by causing the temperature of theincrements of the preform rod to be sufficiently high to allowstraightening of each increment of the preform rod upon continuousengagement of the roller with the periphery of said each increment ofthe preform rod while rotating for a predetermined time which willinsure circularity of said increment; carriage means for moving saidroller and said heating means in a direction parallel to the axis ofrotation of the preform rod; transverse moving means for moving saidroller inward toward the rod axis of rotation, and control means whichis effective, while said carriage means is causing said roller to bemoved parallel to the axis of rotation, for causing said roller (a) tobe moved continuously inwardly toward the axis of rotation to areference point spaced outside the largest expected radial distancewhich distance is measured from the axis of rotation to an outer surfaceof the preform rod and then (b) to be moved in a first mode of contact,in incremental steps of forward and then inward movement toward the axisof rotation until a portion of the preform rod and said roller engageeach other along a portion of the circumference, said transverse movingmeans including;(1) an arm having first and second end portions withsaid roller being supported at said first end portion of said arm; (2)reciprocally movable means which move cyclically toward and away fromthe axis of rotation of the preform rod for supporting pivotally saidarm; (3) first electrical contact means mounted on said reciprocallymoveable means adjacent to said second end portion of said arm; (4)second electrical contact means mounted at said second end portion ofsaid arm and spaced from said first contact means, which secondelectrical contact means upon a movement in a first direction through agap between said first and second contact means is caused to engage saidfirst contact means, said second contact means engageable with saidfirst contact means when said roller has been moved into suitableengagement with the preform rod as said reciprocally moveable means isbeing moved toward the axis of the rotation of the preform rod; and (5)biasing means for biasing said roller toward the axis of rotation andbeing effective upon disengagement of a portion of the preform rod fromsaid roller for causing said second contact means to become spaced fromsaid first contact means; control means, effective as the rotation ofthe preform rod causes a portion of the preform rod which is at a lesserdistance from the axis of rotation than a preceding adjacent portion ofthe preform rod to move away from said roller, for causing the roller tobe moved further gradually and incrementally forward and inward in asecond mode of contact toward the axis of rotation in incremental stepswhich are substantially less than the steps of the first mode until saidroller has remained in continuous engagement with a predeterminedportion of the periphery of an increment of length of the preform rod asthe preform rod is caused to be rotated which predetermined portion issufficient to insure that the increment of length of the preform rod isdisposed concentrically about the axis of rotation; and means forcooling the roller to establish subsequently a setting of the glass ofsuccessive increments of length of the preform rod, after saidsuccessive increments of length have been straightened.
 2. The apparatusof claim 1, wherein said arm is mounted pivotally about a fulcrum onsaid reciprocally moveable means with the distance from said secondcontact means to the fulcrum and from the fulcrum to the end of saidfirst end portion of said arm being such that sufficient engagement ofsaid roller with the preform rod causes the roller to be moved inwardlyto cause said second contact means to be moved through the gap andengage said first contact means.
 3. The apparatus of claim 2, whereinsaid first and second contact means cooperate to provide a stop for theinward movement of said roller after said roller has engaged the preformrod.
 4. The apparatus of claim 3, which includes means attached to saidreciprocally moveable means for limiting the movement of said second endportion of said arm in a direction away from said first contact means.5. The apparatus of claim 4, wherein said reciprocally moveable meanscomprises a platform and said arm is mounted pivotally on said platform,said platform moveable vertically in a direction toward and away fromthe preform rod, and said biasing means including a counterweightpositioned between the fulcrum of said arm and said second contactmeans.
 6. The apparatus of claim 5, wherein said heating means comprisesan oxy-hydrogen torch and means for causing a supply of hydrogen andoxygen to said torch to be at the rate of about 130 liters per minuteand 65 liters per minute, respectively, said carriage means beingadvanced at a speed in the range of about 8 to 10 cm per second and thepreform rod being turned rotatably at about 75 rpm.
 7. The apparatus ofclaim 6, wherein said control means is responsive to the passage of apredetermined time after said roller has been in engagement with apredetermined portion of the periphery of the preform rod, for causingsaid roller to become disengaged from the preform rod and immediatelythereafter moved in another cycle of operation toward the axis ofrotation of the preform rod.
 8. The apparatus of claim 6, wherein saidcontrol means is such that after said roller has been in continuousengagement with the preform rod for a predetermined portion of theperiphery of the preform rod, said control means causes said roller toremain spaced a fixed distance from the axis of rotation as the rolleris moved along the length of the preform rod.